In the electrodeionization water purification device heretofore put to practical use, basically a mixture ion exchange resin of an anionic exchange resin and cationic exchange resin is filled as an ion exchanger into a gap formed by cation and anion exchange membranes to form a depletion chamber, water to be treated is passed through the ion exchange resins, a direct current is allowed to act in a right angle direction with respect to the water to be treated via both the ion exchange membranes, and ions in the water to be treated are electrically discharged into concentrate flowing outside both the ion exchange membranes to produce deionized water. Since impurity ions in the water to be treated are electrically removed by this operation, the deionized water can continuously be obtained without regenerating the filled ion exchange resins by chemical.
Since the regeneration by the chemical is unnecessary in the electrodeionization water purification device, the running cost is determined by power consumption. The power consumption excluding rectification loss in converting an alternate current into a direct current in the electrodeionization water purification device is represented by direct current between both electrodes×voltage. Here, the direct current is determined by the amount of ions contained in the water to be treated, type of the ions, and required treated water quality. That is, in the electrodeionization water purification device, it is necessary to continuously discharge the ions captured by the ion exchange resins in the depletion chamber to the concentrate side by electric migration. A given or more current necessary for the migration of the ions is essential for the electrodeionization water purification device to normally exhibit its performance, therefore, in an ordinary case, in the electrodeionization water purification device, a constant-current operation is performed to hold a constant current value which exceeds a minimum necessary current value in operation conditions. On the other hand, the voltage is determined by electric resistance between the electrodes, and depends largely on capabilities of the ion exchange membranes and ion exchange resins used in the electrodeionization water purification device. That is, the electric resistance is a total sum of electric resistances by an electrode chamber disposed between the electrodes, concentrate chamber, and depletion chamber. When a distance between the electrodes and operation temperature are set to be constant, the electric resistance is influenced by the concentration and type of ions contained in electrode water and concentrate, type of ion exchange membranes and ion exchange resins, type of counter ions of an ion exchange group of the ion exchange resin, further filling method (single or mixed bed), and further contact resistance in an interface of all these electric resistance constituting elements. For the electric resistance constituting elements, the concentration and type of the ions contained in the electrode water and concentrate are determined by the quality of the water to be treated and the required treated water quality, and other elements depend on the capability and use method of the ion exchanger for use in the electrodeionization water purification device.
However, in the conventional electrodeionization water purification device, for the ion exchange resin filled into a electrodeionization module, a general-purpose product widely available is used as such. Minimization of the electric resistance value for reducing the running cost of the electrodeionization water purification device has not been taken into consideration in selecting the ion exchange resins. That is, in the conventional electrodeionization water purification device, as the ion exchange resin, in general, a spherical resin having a diameter of about 0.2 to 0.5 mm is filled which is obtained by introducing into a copolymer of styrene and divinylbenzene (DVB), sulfonic acid group (R—SO3−H+) as a cationic exchange group and a quaternary ammonium base (R—N+R1R2R3) as an anionic exchange group. In this case, the current transfer in ion exchange resin particles, that is, the transfer of electrons and ions transmitted with low resistance via the ion exchange groups which uniformly and densely exist in a polymer gel. On the other hand, in an ion exchange resin particle interface, during movement of the ions and electrons, for the ions, a migration distance of the ions in water is long. For the electrons, an electron transmission path via hydrogen bond among water molecules is long. Moreover, since a contact area of the particles is small because of the spherical shape, a flow of ions is concentrated on a contact portion. This inhibits the current transmission, that is, causes the electric resistance, and this is a major factor of the electric resistance ascribed to the ion exchange resin.
Moreover, since the general-purpose ion exchange resin is filled into the depletion chamber in the conventional electrodeionization water purification device, considerable time and labor are necessary for the manufacture of the device. Especially, to assemble an electrodeionization module, a plurality of sandwiched ends are laminated/bonded using an adhesive, while wetted ion exchange resins have to be uniformly filled. The production requires considerable skills and is not easily automated. Moreover, even when the adhesive is not used, it is difficult to handle the wetted ion exchange resin.
To solve these problems, for example, there have been proposed: a porous ion exchanger which has a porous structure using binder polymer to bond the ion exchange resin and which holds specific water permeability (Japanese Patent Application Laid-Open Nos. 1996-252579, 1998-192716); a depletion chamber structure in which an adhesive is used to integrally bond/form anion and cation exchangers and which obviates necessity of a frame including a specific structure of a liquid passing portion and permeate seal-up portion or an ion exchange membrane (Japanese Patent Application Laid-Open No. 2000-218137); and a simplified structure in which a porous structure is formed in surface portions of cationic and anionic exchange membranes, the cationic exchange membrane is brought into contact with the anionic exchange membrane, and a porous portion of the porous structure is used as a channel for circulating the water to be treated (Japanese Patent Application Laid-Open No. 1999-192491).
When the porous structure described in the Japanese Patent Application Laid-Open No. 1996-252579 is used as a filler of the electrodeionization module, the problem in manufacturing the device is solved concerning the uniform filling of the granular ion exchange resin. However, in the porous structure, the granular ion exchange resins heretofore filled into the electrodeionization module as such are bonded using the binder polymer to form the porous structure. Furthermore, depending on the circumstances, a new step of introducing the ion exchange group also into a binder polymer portion is necessary in manufacturing the porous structure. Although a device assembly step is simplified, the manufacturing of the depletion chamber filler is complicated. Furthermore, it cannot be said that the high electric resistance resulting from the filling of the granular ion exchange resins is sufficiently improved in the porous structure. That is, in the porous structures, the ion exchange group does not exist in the binder polymer portion. Even when the group exists, a matrix material of the binder polymer and the structure of the ion exchange group are different from those of the ion exchange resin portion. Additionally, presence density of the ion exchange groups in the binder polymer is lower than that of the ion exchange resin portion, and it is difficult to form a homogeneous ion exchanger as a whole. Therefore, the problem of nonuniformity of ion or electron movement in the filling layer remains to be unsolved, and it cannot be said that the reduction of the electric resistance of the ion exchanger filling layer and efficient discharge of the captured ions into a concentrate chamber are sufficient.
As described above, for any one of the conventional porous ion exchangers, the granular ion exchange resins are bonded by the binder polymer to form the integral structure, or the porous structure is not concretely described. Moreover, an open cell structure is not disclosed which is manufactured by highly dispersed phase emulsifying polymerization and which includes interconnected macropores and mesopores as a water channel existing on the macropores. In Japanese Patent Publication No. 1992-49563, a porous polymer is disclosed which is manufactured by the highly dispersed phase emulsifying polymerization and which has enhanced adsorption capacity for aqueous or organic acids. However, the porous polymer has an excessively high swelling or liquid absorption capability and is not suitable for producing the deionized water.
Moreover, as a solid acid catalyst, a silica alumina compound such as zeolite, heteropoly acid, cation exchange resin, and the like have heretofore been known. When the catalysts excluding the cation exchange resin are used in a water-containing system, activity is remarkably lowered or the catalysts are dissolved and cannot be used. Therefore, most of the solid acid catalysts for use in the water-containing system are the cationic exchange resins.
It is known that a particle diameter of the cation exchange resin may be reduced in order to enhance the catalyst activity of the cation exchange resin. However, to fill the cationic exchange resin into a reaction tower and continuously supply a liquid to be treated, when a particle diameter is reduced, a transmission resistance of the liquid to be treated increases. While large catalyst activity is maintained, a treatment amount cannot be raised. Moreover, as a method of further efficiently allowing the reaction to proceed, a method using reaction distillation is known. However, when the conventional granular cationic exchange resin is used as the solid acid catalyst for reaction distillation, the filling of the cationic exchange resin into a distillation tower remarkably blocks transmission property of a gas or liquid including a raw material or reaction product. Therefore, it has been difficult to apply the resin to the reaction distillation.
Therefore, as a method of solving this shortcoming, there have been proposed: a method of granulating the cation exchange resin (Japanese Patent Publication No. 1987-42658); a method of filling an ion exchange fiber (Japanese Patent Application Laid-Open No. 1982-7259); and a method of introducing the ion exchange group onto a base substance manufactured by graft polymerization to have a sufficient void (Japanese Patent No. 2846975).
However, the method of granulating the cation exchange resin has a disadvantage that improvement effect of the transmission property of the gas or liquid is not sufficient and reaction speed drops because of granulation. Moreover, in the method of filling the ion exchange fiber, the reaction speed does not drop, but the fiber and fiber processed materials such as woven cloth are excessively soft, have insufficient strength, and therefore have a disadvantage that they absorb reaction liquid and are deformed and hinder the transmission of gas. For the method of introducing the ion exchange group onto the base substance manufactured by the graft polymerization to have sufficient void, an improvement effect is recognized as a method of compensating for mechanical strength shortage which is the disadvantage of the method of filling the ion exchange fiber. However, the amount of ion exchange groups which can be introduced by radiation graft polymerization is limited. Therefore, there is a disadvantage that an ion exchange capacity is not a dequate, and the reaction rate is restricted. As described above, in the conventional technique, the ion exchangers having various shapes as the solid acid catalysts have been proposed. However, although sufficiently high catalyst activity is maintained, rapid improvement of transmission property for the gas or liquid including the raw material or reaction product is not achieved.
Moreover, as the porous structure which includes the open cell structure including the interconnected macropores and mesopores existing on the walls of the macropores and which further includes the micropores existing on the inner walls of the open cell, an inorganic porous structure constituted of silica, etc. is known (U.S. Pat. No. 5,624,875). Furthermore, active application development of the inorganic porous structure as the filler for chromatography has been performed. However, since the inorganic porous structure is hydrophilic, a laborious operation involving cost increase, such as a hydrophobic treatment of the surface, has been necessary for using the structure as adsorbent. Additionally, when the inorganic porous structure is held in water for a long time, a silicate ion generated by hydrolysis of silica is eluted into water. Therefore, it has been impossible to use the structure as the ion exchanger for manufacturing pure water or ultrapure water. On the other hand, it has been reported that with the use of the inorganic porous structure as the filler for chromatography, the capability can remarkably be enhanced as compared with the use of the conventional granular filler. However, since the mesopore has a diameter of 50 μm at maximum in the manufacturing method, there is a restriction during the treatment of a large flow rate at low pressure. Moreover, the micropore also has a diameter of about 100 nm at maximum. Therefore, in separation of a polymer compound such as protein and enzyme, there is a problem that a polymer amount component is insufficiently fractionated.
On the other hand, as an organic porous structure including continuous pores, a porous structure including a particle aggregation structure is disclosed in F. Svec, Science, 273, 205 to 211 (1996), and the like. However, since the porous structure obtained in this method includes the particle aggregation structure, a pore volume is small, the mesopore cannot be enlarged, and therefore there has been the restriction during the treatment of the large flow rate at the low pressure. Moreover, since the presence of micropores is unclear and specific surface area is small, adsorption capacity is low with the use as the adsorbent, and it has been difficult to fractionate polymer compounds by molecular weight when the organic porous structure is used as the filler for chromatography.